At its nearest, northern Australia is just over 400 km from an active convergent plate margin. This complex and unique tectonic region combines active subduction and the collision of the Sunda-Banda Arc with the Precambrian North Australian Craton (NAC) near the Timor Trough and continues through to the New Guinea Highlands. Ground-motions generated from earthquakes on these structures have particular significance for northern Australian communities and infrastructure projects, with several large earthquakes in the Banda Arc region having caused ground-shaking-related damage in the northern Australian city of Darwin over the historical period. There are very few, if any, present-day tectonic analogs where cold cratonic crust abuts a convergent tectonic margin with subduction and continent-continent collision. Ground motions recorded from earthquakes in typical subduction environments are highly attenuated as they travel through young sediments associated with forearc accretionary prisms and volcanic back-arc regions. In contrast, seismic energy from earthquakes in the northern Australian plate margin region are efficiently channelled through the low-attenuation NAC, which acts as a waveguide for high-frequency earthquake shaking. As such, it is difficult to select models appropriate to the region for seismic hazard assessments. The development of a far-field ground-motion model to support future seismic hazard assessments for northern Australia is discussed. In general, the new model predicts larger ground motions in Australia from plate margin sources than models used for the 2018 National Seismic Hazard Assessment of Australia, none of which were considered fully appropriate for the tectonic environment. Short-period ground motions are strongly dependent on hypocentral depth and are significantly higher than predictions from commonly-used intraslab ground-motion models at comparable distances. The depth dependence in ground motion diminishes with increasing spectra periods. <b>Cite this article as</b> Allen, T. I. (2021). A Far-Field Ground-Motion Model for the North Australian Craton from Plate-Margin Earthquakes, <i>Bull. Seismol. Soc. Am. </i><b> 112</b>, 1041–1059, doi: 10.1785/0120210191

A database of recordings from moderate-to-large magnitude earthquakes is compiled for earthquakes in western and central Australia. Data are mainly recorded by Australian National Seismograph Network (ANSN), complemented with data from temporary deployments, and covering the period of 1990 to 2019. The dataset currently contains 1497 earthquake recordings from 164 earthquakes with magnitudes from MW 2.5 to 6.1, and hypocentral distances up to 1500 km. The time-series data are consistently processed to correct for the instrument response and to reduce the effect of background noise. A range of ground-motion parameters in the time and frequency domains are calculated and stored in the database. Numerous near-source recordings exceed peak accelerations of 0.10 g and range up to 0.66 g, while the maximum peak velocity of the dataset exceeds 27 cm/s. In addition to its utility for engineering design, the dataset compiled herein will improve characterisation of ground-motion attenuation in the region and will provide an excellent supplement to ground-motion datasets collected in analogue seismotectonic regions worldwide. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

Public concerns have been raised about the potential for induced seismicity as state and territory governments lift moratoriums on hydraulic stimulation activities for the exploration and extraction of unconventional hydrocarbons. The Scientific Inquiry into Hydraulic Fracturing in the Northern Territory articulated the need for a traffic-light system “to minimise the risk of occurrence of seismic events during hydraulic fracturing operations” within the Beetaloo Sub-basin. A temporary seismic network (Phase 1) was deployed in late 2019 to monitor baseline seismic activity in the basin. Based on the data analysed herein (November 2019 – April 2021), no seismic events were identified within the area of interest suggesting that the Beetaloo Sub-basin is largely aseismic. Observations to date indicate that there is potential to identify events smaller than ML=1.5 within the basin. The recent installation of ten semi-permanent stations for continuous real-time monitoring will contribute to ongoing baseline monitoring efforts and support the implementation of an induced seismicity traffic-light system. The outcome of this study will be used to build knowledge about potential human-induced seismic activity in the region that may be associated with unconventional hydrocarbon recovery. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

The Mwp 6.1 Petermann Ranges earthquake that occurred on 20 May, 2016 in the Central Ranges, NT, is the largest onshore earthquake to be recorded in Australia since the 1988 Tennant Creek sequence. While geodetic and geophysical analyses have characterized the extent of surface rupture and faulting mechanism respectively, a comprehensive aftershock characterization has yet to be performed. Data has been acquired from a 12-station temporary seismic network deployed jointly by the ANU and Geoscience Australia (GA), collected from five days following the mainshock to early October. Taking advantage of enhanced automatic detection techniques using the SeisComP3 real-time earthquake monitoring software within the National Earthquake Alerts Centre (NEAC) at GA, we have developed a comprehensive earthquake catalogue for this mainshock-aftershock sequence. Utilising the NonLinLoc location algorithm combined with a Tennant Creek-derived velocity model, we have preliminarily located over 5,800 aftershocks. With additional spatio-temporal analyses and event relocation, our objective will be to use these aftershocks to help delineate the geometry of the headwall rupture along the Woodroffe Thrust. These high-resolution aftershock detection techniques are intended to be implemented in real-time within the NEAC following future significant Australian intraplate earthquakes. This paper was presented at the Australian Earthquake Engineering Society 2021 Virtual Conference, Nov 25 – 26.

Geoscience Australia and the NSW Department of Industry undertook seismic monitoring of the NSW CSG extraction area in Camden as well as baseline monitoring in the region between 2015 and 2019. Geoscience Australia established and maintained seismic stations to identify of events of greater than ML2.0 within the CSG fields. Three new seismic stations were located near Camden CSG area with two baseline stations in North-West Sydney. This poster details the station builds and seismic monitoring of both the Camden CSG production area and the wider region during the project.

Geoscience Australia provides 24/7 monitoring of seismic activity within Australia and the surrounding region through the National Earthquake Alerts Centre (NEAC). Recent enhancements to the earthquakes@GA web portal now allow users to view felt reports, submitted online – together with reports from other nearby respondents – using the new interactive mapping feature. Using an updated questionnaire based on the US Geological Survey’s Did You Feel It? System, Geoscience Australia now calculate Community Internet Intensities (CIIs) to support near-real-time situational awareness applications. Part of the duty seismologists’ situational awareness and decision support toolkit will be the production of real-time “ShakeMaps.” ShakeMap is a system that provides near-real-time maps of shaking intensity following significant earthquakes. The software ingests online intensity observations and spatially distributed instrumental ground-motions in near-real-time. These data are then interpolated with theoretical predictions to provide a grid of ground shaking for different intensity measure types. Combining these predictions with CIIs provides a powerful tool for rapidly evaluating the likely impact of an earthquake. This paper describes the application of the new felt reporting system and explores its utility for near-real-time ShakeMaps and the provision of situational awareness for significant Australian earthquakes.

Modern geodetic and seismic monitoring tools are enabling the study of moderate-sized earthquake sequences in unprecedented detail. Discrepancies are apparent between the surface deformation envelopes ‘detectable’ using these tools, and ‘visible’ to traditional ground-based methods of observation. As an example, we compare the detectible and visible surface deformation caused by a sequence of earthquakes near Lake Muir in southwest Western Australia in 2018. A shallow MW 5.3 earthquake on the 16th of September 2018 was followed on the 8th of November 2018 by a MW 5.2 event in the same region. Focal mechanisms for the events suggest reverse and strike-slip rupture, respectively. Interferometric Synthetic Aperture Radar (InSAR) analysis of the events suggests that the ruptures are in part spatially coincident and deformed the Earth’s surface over ~ 12 km in an east-west direction and ~ 8 km in a north-south direction. Field mapping, guided by the InSAR results, reveals that the first event produced an approximately 3 km long and up to 0.5 m high west-facing surface rupture, consistent with slip on a moderately east-dipping fault. No surface deformation unique to the second event was identifiable on the ground. New rupture length versus magnitude scaling relationships developed for non-extended cratonic regions as part of this study allow for the distinction between ‘visible’ surface rupture lengths (VSRL) from field-mapping and ‘detectable’ surface rupture lengths (DSRL) from remote sensing techniques such as InSAR, and suggest longer ruptures for a given magnitude than implied by commonly used scaling relationships.

Damaging earthquakes in Australia and other regions characterised by low seismicity are considered low probability, high consequence events. Uncertainties in modeling earthquake occurrence rates and ground motions pose unique challenges to forecasting seismic hazard in these regions. In 2018 Geoscience Australia released its National Seismic Hazard Assessment (NSHA18). Results from the NSHA18 indicate significantly lower seismic hazard across almost all Australian localities at the 1/500 annual exceedance probability (AEP) relative to the factors in the Australian earthquake loading standard; the AS1170.4. Due to concerns that the 1/500 AEP hazard factors proposed in the NSHA18 would not assure life safety throughout the continent, the amended AS1170.4 (revised in 2018) retains seismic demands developed in the early 1990s and also introduces a minimum hazard design factor of Z = 0.08 g. The hazard estimates from the NSHA18 have challenged notions of seismic hazard in Australia in terms of the probability of damaging ground motions and raises questions as to whether current practices in probabilistic seismic hazard analysis (PSHA) deliver the outcomes required to protect communities in low-seismicity regions, such as Australia. By contrast, it is also important that the right questions are being asked of hazard modelers in terms of the provision of seismic demand objectives that are fit for purpose. In the United States and Canada, a 1/2475 AEP is used for national hazard maps due to concerns that communities in low-to-moderate seismicity regions are considerably more at risk to extreme ground-motions. The adoption of a 1/2475 AEP seismic demands within the AS1170.4 would bring it in to line with other international building codes in similar tectonic environments and would increase seismic demand factors to levels similar to the 1991 hazard map. This, together with other updates, may be considered for future revisions to the standard. Presented at the Technical Sessions of the 2021 Seismological Society of America Annual Meeting (SSA)

There has been a long-identified need in New Zealand for a community-developed three-dimensional model of active faults that is accessible and available to all. Over the past year, work has progressed on building and parameterising such a model – the New Zealand Community Fault Model (NZ CFM). The NZ CFM will serve as a unified and foundational resource for many societally important applications such as the National Seismic Hazard Model, Resilience to Natures Challenges Earthquake and Tsunami programme, physics-based fault systems modelling, earthquake ground-motion simulations, and tsunami hazard evaluation. Version 1.0 of the NZ CFM is nearing finalisation and release. NZ CFM v1.0 provides a simplified 3D representation of New Zealand’s crustal-scale active faults (including some selected potentially active faults) compiled at a nominal scale of 1:500,000 to 1:1,000,000. NZ CFM faults are defined based on surface traces, seismicity, seismic reflection profiles, wells, and geologic cross sections. The model presently incorporates more than 800 objects (i.e., faults), which include triangulated surface representations of those faults and associated parameters such as dip and dip direction, seismogenic rupture depth, sense of movement, slip direction, and net slip rate. Presented at the 2021 New Zealand Society for Earthquake Engineering (NZSEE) Conference (https://www.nzsee.org.nz/event/2021-nzsee-conference/)

We present earthquake ground motions based upon a paleoseismically-validated characteristic earthquake scenario for the ~ 48 km-long Avonmore scarp, which overlies the Meadow Valley Fault, east of Bendigo, Victoria. The results from the moment magnitude MW 7.1 scenario earthquake indicate that ground motions are sufficient to be of concern to nearby mining and water infrastructure. Specifically, the estimated median peak ground acceleration (PGA) exceeds 0.5 g to more than ~ 10 km from the source fault, and a 0.09 g PGA liquefaction threshold is exceeded out to approximately 50-70 kilometres. Liquefaction of susceptible materials, such as mine tailings, may occur to much greater distances. Our study underscores the importance of identifying and characterising potentially active faults in proximity to high failure-consequence dams, including mine tailings dams, particularly in light of the requirement to manage tailing dams for a prolonged period after mine closure. Paper presented at Australian National Committee on Large Dams (ANCOLD) conference 2020, online. (https://leishman.eventsair.com/ancold-2020-online/)